1. Field of the Invention
This invention relates to a danger deciding apparatus for a motor vehicle and an environment monitoring apparatus for a motor vehicle. More specifically, this invention relates to a danger deciding apparatus for a motor vehicle for detecting the approaching degree of an approaching object in a picked-up image of an environment of the vehicle to decide the danger of contact or collision (hereinafter simply referred to contact) with the approaching object, and an environment monitoring apparatus for monitoring the environment of the vehicle to decide the danger of contact with the approaching object.
2. Description of the Related Art
For example, when a driver of a vehicle running on a road of one-side two or more lanes of e.g. a speed way intends to change his running lane, if he changes the lane while he is missing a vehicle which catches up with his own vehicle on another lane at a higher speed than his own vehicle from the rear-side direction, there is strong possibility of a serious accident.
When the following vehicle on the same lane abruptly approaches his own vehicle from the rear-side direction, if the driver makes abrupt braking, there is possibility of bumping-into-the back. Therefore, it is desired that the driver surely notices or recognizes other vehicles in the environment.
A technique for avoiding the danger as described above has been proposed as an environment monitoring system for a vehicle in JP-A-7-50769. Now referring to FIGS. 8A-8D, an explanation will be given of this environment monitoring system.
FIGS. 8A-8C are views for explaining a change in a rear/rear-side direction (hereinafter referred to as rear-side direction) image acquired by a video camera 1. FIG. 8A shows a status inclusive of the vehicle concerned. FIG. 8B shows an image acquired by a video camera 13 at timing t in an environment of the vehicle concerned. FIG. 8C shows an image acquired at timing t+.DELTA.t.
Now it is assumed that the vehicle concerned is running straight on a flat road. The road sign and building residing in the rear of the vehicle concerned in FIG. 8A are observed as images shown in FIGS. 8B and 8C at timings t and t+.DELTA.t, respectively. Coupling the corresponding points in these two images provides speed vectors as shown in FIG. 8D. There are referred to as "optical flows".
It can be seen that the optical flows radially appear from an FOE (Focus of Expansion) where the road disappears. While the vehicle concerned runs, the optical flows of an object which leaves from the vehicle concerned are vectors in a direction converging toward the FOE. The optical flows on the object which approaches toward the object concerned are vectors in a direction diverging from the FOE.
Therefore, a conventional environment monitoring system detects the optical flows by processing the rear-side direction image acquired by a camera 13, and uses to monitor the relationship between the vehicle concerned and the following vehicle or another vehicle running on an adjacent lane to detect the other vehicle approaching the vehicle concerned, thereby deciding danger of the contact of the vehicle concerned with the approaching object.
In some prior arts, a technique of searching corresponding points using two cameras is adopted. Specifically, an edge point Pa (not shown) of an object is detected in a rear-side direction image acquired by the one camera. A point Pb (not shown) of the image acquired by another camera corresponding to the detected edge point Pa is detected. The position P of the object is acquired by the pixel coordinates of Pa and Pb. On the basis of the position P of the approaching object acquired, the existence of the approaching object such as another vehicle approaching the vehicle concerned is detected and danger of contact of the approaching object is decided.
As an alternative technique, cameras are installed to be oriented toward both left-side and right-side directions in the front or rear portion of the vehicle, and the images in both left-side and right-side directions acquired by the cameras are processed in the manner similar to the above rear-side direction image. When the vehicle concerned approaches a side road intersecting the vehicle concerned such an approaching an intersection or outgoing from the garage facing a road, the existence of the approaching object such as a man or another vehicle approaching from the side road is detected and danger of collision of the vehicle concerned with the approaching object is decided.
In the environment monitoring apparatus for a vehicle, in order to recognize an approaching object in the environment, the camera(s) may be located at various points other than the points where the rear-side direction image or side direction images can be acquired.
However, the above prior art environment monitoring apparatus individually makes image processing according to the installed position of the camera to detect the approaching object. Specifically, where both of rear-side monitoring and side monitoring are intended simultaneously, two CPUs therefor are prepared separately. The one is intended for processing the rear-side direction image to detect the approaching object from the rear-side direction. The other is intended for processing the side direction image to detect the approaching object from the side direction. Where extension of the monitoring range is intended by provision of cameras in various directions, plural CPUs for image processing must be prepared. This is problematic from the standpoint of cost.
In order to solve the above problem, it can be proposed to make image processing for plural images sequentially using a single CPU. However, this lengthens the time required for image processing, thereby deteriorating the accuracy of detecting the approaching object. Thus, it is not possible to detect danger of contact with an environmental approaching object.